A wide variety of semiconductor chips having integrated circuits (IC) are known in the industry. Some examples of IC's include Application Specific Integrated circuits (ASIC) and, Application Specific Standard Product (ASSP). In general, ICs and their packages have been becoming more complex over time, with the result that their power, speed and/or their size has been increasing. Also, ICs are generally attached by having a number of leads that are each individually soldered onto a mounting location of a circuit board or other base component. In some instances, all of these soldered connections may end up not being properly made. This can be particularly true if the IC is not properly flat, since it is generally being mounted to a flat mounting surface.
Warping refers to a bending or twist or general lack of flatness in overall IC package, including particularly the plane formed by the solder joint locations. A lack of flatness in an IC package can cause various problems such as poor soldered joints between the IC package and the mounting surface, poor or no contact at the solder joint, undesirably pillowed joints, or intermittent contact at the solder joints. Lack of flatness can occur where the entire package warps so that it is curved or bent or otherwise non-flat. The desired flatness can in some cases be to a very high tolerance. For example, in some application such as in the context of some BGA packages, a maximum warping tolerance of approx 0.008 inches is desired.
The problem of IC package warping often occurs during the soldering process, also known as reflow, and any re-work of the same. The problem can be exacerbated in larger packages due to the larger size, and is also exacerbated when soldering temperatures become higher. Recently, the use of lead-free solders has become more prevalent on certain product types. This lead-free solder generally requires a higher soldering temperature than prior solders thus potentially exacerbating IC package warpage.
One prior solution to the problem of IC package warping has been the incorporation on top of the IC of a flat stiffener plate that is permanently affixed to the top surface of the IC. The stiffener plate takes the form essentially of a completely flat entirely planar item having a constant thickness, and is a simple rectangle having approximately its perimeter be the size of the IC package perimeter when viewed from the top. A central region of the flat stiffener plate may be cut out. However, these stiffener flat plates suffer from the disadvantage that they themselves are entirely flat, and thus, have a somewhat limited resistance to warping due to temperature change or torsion or bending forces. In order to make a flat plate strong enough to provide desirable resistance to warping in the overall IC package, it can be necessary to make the stiffening plate undesirably thick. It is undesirable for the stiffening plate, which rests on top of the IC, to be too thick because the thick stiffening plate, on top of and added to the IC thickness, causes the entire assembled IC package to be thick, which can be undesirable if the total IC package becomes too thick. thus potentially limiting IC packaging placement options and/or increasing printed circuit card to printed circuit card separation in the final system assembly. Moreover, the added stiffener thickness increases the IC die to lid spacing, thereby creating a larger separation that needs to be filled with Thermal Interface Material, ultimately impeding thermal dissipation from the IC. Moreover, because of the stiffener's entirely flat cross-sectional profile, increased stiffness is achieved inefficiently though the increase of the overall volume of material, thus adding additional cost and weight to the final IC package. Therefore, there is a need in the art for stiffening of IC packages that can provide improved performance and/or mounting reliability while providing a desirable low degree of thickness and/or a desirable low amount of material in the eventual fully installed IC package.